In this paper, we prove that the connectivity and the edge connectivity of the lexicographic product of two graphs G1 and G2 are equal to κ1v2 and min{λ1v 2 2 , δ2 +δ1v2}, respectively, where δi, κi, λi and vi denote the minimum degree, the connectivity, the edge-connectivity and the number of vertices of Gi, respectively. We also obtain that the edge-connectivity of the direct product of K2 an...

We characterize graphs of large enough order or large enough minimum degree which contain edge cuts whose deletion results in a graph with a specified number of large components. This generalizes and extends recent results due to Ou (Edge cuts leaving components of order at least m, Discrete Math. 305 (2005), 365-371) and Zhang and Yuan (A proof of an inequality concerning k-restricted edge con...

Let G = (V,E) be a k-edge-connected graph with edge costs {c(e) : e ∈ E} and let 1 ≤ l ≤ k − 1. We show by a simple and short proof, that G contains an l-edge cover I such that: c(I) ≤ l k c(E) if G is bipartite, or if l|V | is even, or if |E| ≥ k|V | 2 + k 2l ; otherwise, c(I) ≤ (

For a connected graph G = (V , E), an edge set S ⊂ E is a k-restricted edge cut if G − S is disconnected and every component of G − S contains at least k vertices. The k-restricted edge connectivity of G, denoted by λk(G), is defined as the cardinality of a minimum krestricted edge cut. For U1,U2 ⊂ V (G), denote the set of edges of Gwith one end in U1 and the other in U2 by [U1,U2]. Define ξk(G...

We present new approaches to constructing graph sparsifiers — weighted subgraphs for which every cut has the same value as the original graph, up to a factor of (1 ± ǫ). Our first approach independently samples each edge uv with probability inversely proportional to the edge-connectivity between u and v. The fact that this approach produces a sparsifier resolves a question posed by Benczúr and ...

A (k; g)-graph is a k-regular graph with girth g. A (k; g)-cage is a (k; g)-graph with the smallest possible number of vertices. In this paper we prove that (k; g)cages are k-edge-connected if k ≥ 3 and g is odd.

The vertex-edge Wiener index of a simple connected graph G is defined as the sum of distances between vertices and edges of G. Two possible distances D_1(u,e|G) and D_2(u,e|G) between a vertex u and an edge e of G were considered in the literature and according to them, the corresponding vertex-edge Wiener indices W_{ve_1}(G) and W_{ve_2}(G) were introduced. In this paper, we present exact form...

the first ($pi_1$) and the second $(pi_2$) multiplicative zagreb indices of a connected graph $g$, with vertex set $v(g)$ and edge set $e(g)$, are defined as $pi_1(g) = prod_{u in v(g)} {d_u}^2$ and $pi_2(g) = prod_{uv in e(g)} {d_u}d_{v}$, respectively, where ${d_u}$ denotes the degree of the vertex $u$. in this paper we present a simple approach to order these indices for connected graphs on ...

We focus on the algorithm underlying the main result of [6]. This is an algebraic formula to generate all connected graphs in a recursive and efficient manner. The key feature is that each graph carries a scalar factor given by the inverse of the order of its group of automorphisms. In the present paper, we revise that algorithm on the level of graphs. Moreover, we extend the result subsequentl...